Apparently they don´t. I have not seen one single carve in that video.

They are similar to the square stubbies, which mainly turn on weight placement back, nothing else. There is a reason why no-one has tried this before: A snow board flexes, a windsurfboard does not. Turning on weight back is kind of forcing a board through the turn rather than flowing through a turn like boards with more rocker do or snowboards. So in my opinion it does not carve unless you´d put a lot of rocker in it and then it will not plane.
I like to use a tapered outline as one of the ways to make a board turn. It helps a lot, especially to initiate the turn where the taper works like a kind of rudder. The more the taper the quicker the reaction to steering impulses. To continue through the turn, the amount of rocker is important.

Interesting. I imagine Victor Fernandez and Adam Lewis might have a different view of their stubbies. Could have sworn I have seen them do the odd carve / bottom turn!

What I meant is that the similarity between MB boards and stubbies is that they turn mostly depending on weight placement. These Stubbies surely carve better as the tail is not as wide and thick and there is some amount of taper in the outline, not much but more than the MB boards with their peanut outline. JP went for more taper in their 2nd version of the Slate.
Taper is not only better to initiate a turn, you also get a bigger wind range, a wider section to get planing and a narrower part the faster you go. I don´t think these MB boards will be very good high wind or wave riding boards with the lift you get of that tail.
Last week I had a guy on holiday in Sotavento with a repair on his Stubbie 77 and he rented a Haka 82 for the time and he said exactly that: Early planing similar but more float/stability in the lulls, more high end control, faster and better turning (probably jibing). The Reaper makes more use of weight placement but the initiation of the turn is helped a lot by some taper. It reacts a lot quicker then stubbies.

My experience is that stubby style boards turn extremely well when you are more reliant on wind and technique rather than wave power. Better in fact than equivalent size more 'tapered' boards.
The combination of short length, flat rocker, relatively narrow width (for volume), soft rails and parallel / wide tails is very effective as an alternative to the more traditional 'tapered' approach.

Also if I was a board manufacturer I'd be keen to try a radical new shape if one of the most innovative windsurfers around was using it so effectively. And certainly before I dismissed it.

Yes, there is an interesting element to having short flat rockered boards with the straps (weight) further back. However I found the stubbies pretty boring to sail, in spite of how different it looked. Not reactive enough for small waves, where they are meant for. You don´t see these guys using them in proper waves either. So with the Reaper I did use a part of this but not too much and still kept some taper. Your super mini is not that square either and is half way between a stubbie and the Reaper. Taper also keeps the nose clear in harder carve with more front foot pressure, if you need/want to, and not catch the rail. Have you tried a Reaper? Then you will see what I mean. Had that board I made for you in 2012(?) as a kind of experiment, had the mast track further back, it would have worked better and been the fore runner of your SM or the Reaper. I should not have done such an experiment with a normal customer but it seemed to be the solution for what you asked for and you were informed it was an experiment.

I have a freestyle guy in southern Germany and he has asked me for quite radical shapes, he was also intrigued by the MB shapes but after testing one he changed his mind. Yes, the length was interesting and I made him a really short board on the base of that but not with such a peanut outline. Balz Müller may be a radical sailor, what he does is in the air and not carving. When they explained the outline for carving (the swiss jibing solution it says at the start), I was expecting to see jibing or carving in the video. But there simply isn´t.

Stubbies were copied from Alaia, Tomo or Vanguard surfboards. They were desperate to have something new for marketing and they pick stuff from surfing, whether it is suitable for windsurfing or not, like has happened before. These surfboards need to have a lot of rocker, more than traditional surfboards. But that is fine as they only need to plane on a wave and if you like that style as they are not very versatile in how to ride them compared to more traditional surfboards. They rely for 90% on the rocker for turning. Then they had to make the windsurfboards with a flat rocker line off course as a windsurfboard needs to plane going out as well. But then in a hard carve with a wide tail and nose and narrower midsection it gets hard to keep the nose clear. So they moved the straps back. So in stead of rocker they turn mostly on weight placement. In my opinion it is too one sided, I prefer to mix with the various elements a shaper can use to make a board turn, for some boards a bit more of this and for others a bit more of that. I bet we´ll see these boards disappear again when the molds have worn down and they need something new. JP already went back a step. As for the MB boards, apart from Balz Müller or the odd freestyler, I have not seen anyone else use one. Sometimes as a brand you also have to look through the marketing BS of other brands. See what can be interesting and leave the rest.

They say when the conditions are not so good - smaller, less powerful waves and more onshore wind - that favours the Stubby. The Grip excels when the waves are better. Yet Victor uses the Grip for Pozo.

I had hoped that Balz would have explained how and why the MB Boards work. His foiling is a great advert for the MB Boards.

I have just got my first stubby, but haven't had enough wind to get much sailing on it yet, but I bought it as a wave/freewave type of board for 3.7 to 5.9 sails, and it feels good so far. My 2016 JP Slate SUP (Tomo type outline) has a lot of rocker and works on a wave but not on flatter water. What Bouke says rings true to me.